1. Field of the Invention
The present invention relates to a semiconductor device, more particularly to a semiconductor device with reduced capacitance between interconnecting lines, and to methods of fabricating such a semiconductor device.
2. Description of the Related Art
As shown in FIG. 6, the interconnecting lines 1 in a conventional semiconductor device, which are embedded in an inter-layer dielectric film 3 formed on a lower wiring layer 2, generally have a rectangular cross-sectional shape. As the facing sides of adjacent interconnecting lines are mutually parallel, they act as parallel plate electrodes, producing considerable electrostatic capacitance between adjacent lines. This so-called interconnect capacitance adversely affects circuit operation.
In Japanese Unexamined Patent Application Publication No. H09-064182, the interconnect capacitance is reduced by giving the interconnecting lines the cross-sectional shape of a parallelogram or ellipse, thereby increasing the distance between the facing sides of adjacent interconnecting lines. Giving the interconnecting lines the cross-sectional shape of a parallelogram, however, requires directional etching in a diagonal direction from the resist film, with attendant problems of poor etching accuracy. For interconnecting lines with an elliptical cross-sectional shape, no detailed description of the etching method is given; practical fabrication is presumably difficult.
In Japanese Unexamined Patent Application Publication No. H06-204350, interconnect capacitance is reduced by cutting away facing corners in the upper or lower parts of adjacent interconnecting lines to widen the distances between those parts of the facing sides. However, the cross-sectional area is reduced by the amount cut away, causing a problem of increased line resistance.
In Japanese Unexamined Patent Application Publication No. H05-109912, interconnect capacitance is reduced by giving the interconnecting lines tapered sides, so that the cross-sectional shape is a trapezoid, the facing sides of adjacent interconnecting lines sloping away from each other. The taper also reduces the cross-sectional area of the interconnecting lines, however, again causing a problem of increased line resistance.